In vivo fibreoptic confocal imaging (FOCI) of the human ocular surface

Recent developments in the miniaturization of confocal imaging technology have resulted in the development of a hand-held confocal microscope probe. There are many structures of interest in the human eye that are within reach of a fluorescence-mode confocal microscope; this study assessed the feasibility of in vivo human ocular imaging. Safety analysis was undertaken to ensure that the laser light applied to the ocular surface structures constituted no threat to patient safety. A fibreoptic confocal imaging (FOCI) probe using an illumination wavelength of 488 nm was applied to the ocular surface of four volunteers after topical administration of sodium fluorescein. Stabilization of the probe on the ocular surface was difficult, but movement artefacts could be minimized to a satisfactory level in most subjects by a variety of procedures. High-quality images of conjunctival epithelial and goblet cells, lamina propria structures, accessory lacrimal glands, lacrimal ducts and superficial sclera were obtained. Lateral resolution was 1–1.5 µm and axial resolution was approximately 30 µm; individual erythrocytes could be seen in conjunctival vessels. The rete ridges and intervening epithelial components, including the probable location of corneal limbal stem cells, could be viewed, although it was not possible to distinguish cell subgroups. The study showed that fluorescence-mode imaging of the ocular surface is a viable and promising tool for assessment of diseases and processes involving superficial ocular structures. Refinement of equipment and techniques, particularly probe stabilization, is necessary to realize fully the potential of FOCI for ocular use.